Scraping Prices Without an API: Chrome Content Script Patterns for Japanese E-Commerce

Short summary

Japanese e-commerce platforms lack shared APIs, causing price discrepancies of ¥5,000–¥30,000 across Amazon.co.jp, Mercari, and Rakuten. This tutorial walks through building a Chrome extension (Arbitra) to scrape real-time pricing: CSS selector fallback chains for resilience, Japanese currency parsing for edge cases, and mutation observers for React-rendered content. Code patterns handle frequent site redesigns and automate product matching across platforms.

• •Extract prices from Japanese e-commerce without APIs using CSS selector fallbacks and fallthrough logic
• •Parse Japanese currency formats (¥, 円, commas, suffixes) and handle out-of-stock markers
• •Use MutationObserver for React SPAs; keep Chrome MV3 service worker calls short to prevent timeout

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